The MAPC sketch accessibility-based travel model piloted in the West Station Area analyzes four trip purposes: home-based work, home-based school, home-based other, and non-home-based; and six travel modes: Walk, bike, auto driver, auto passenger, transit (walk access), and transit (drive access).
The sketch travel model is organized into seven steps. The steps are described briefly below. Then maps showing the results of steps 3 through 7 are presented for the West Station existing conditions analysis to demonstrate the workflow and relationships among the steps.
Skim cleaning - csv files containing OD travel costs are processed into a standard format for consistency across all scenarios.
Import skims - standardized OD skim csv files are imported into emma’s Skim class.
Summarize accessibility - skim files, land use data, and decay curves are used to calculate access to total jobs, retail jobs, and school enrollments from origin zones and access from households by vehicle ownership and income to destination zones.
Trip generation - land use data are used to estimate person trip productions and attractions by TAZ. In the immediate vicinity around the West Station Area (referred to as the “Window” area), trips are disaggregated from TAZ level to census block level.
Mode choice - Accessibility and demographic data are used to estimate the proportion of trips made by different modes. Mode shares are estimated separately for trip productions and attractions. They are applied to trip generation estimates to develop an initial estimate of trips by mode.
Distribution - Trip productions and attractions by mode are matched into OD pairs based on generalized OD costs. The resulting trip table is balanced using iterative proportional fitting to ensure total trip productions and attractions in each zone match trip generation estimates.
TNC trips - Transportation Network Company (TNC) trips are estimated based on distribution results, estimated TNC costs, and assumptions about which trips are likely to switch to TNC.
In this step, access to and from various activities and population groups is estimated for TAZ’s and blocks (for walking and biking in the window area only). The example maps below reflect access to all jobs by walking, biking, transit (walk access), and car under existing conditions, using decay rates for the home-based work travel purpose.